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A249065 Numbers n such that n = concatenate(a, b) and sigma(a) + sigma(b) = phi(n). 1

%I #5 Nov 01 2014 02:19:20

%S 12,420,966,2700,5700,5940,7440,12540,71100,76680,107880,118680,

%T 121920,156420,160650,161880,259080,284580,339150,353430,395850,

%U 498420,585200,600780,701220,746130,752100,771420,870870,1052220,1249680,1654620,1684020,1696080

%N Numbers n such that n = concatenate(a, b) and sigma(a) + sigma(b) = phi(n).

%e For n = 966 we can consider 966 as 96 U 6; sigma(96) + sigma(6) = 252 + 12 = 264 = phi(966).

%p with(numtheory); P:=proc(q) local a,b,i,n; for n from 1 to q do

%p for i from 1 to ilog10(n) do a:=trunc(n/10^i); b:=n-a*10^i;

%p if sigma(a)+sigma(b)=phi(n) then print(n); break;

%p fi; od; od; end: P(10^9);

%Y Cf. A000005, A000203, A239562.

%K nonn,base

%O 1,1

%A _Paolo P. Lava_, Oct 20 2014

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Last modified March 28 04:13 EDT 2024. Contains 371235 sequences. (Running on oeis4.)